1. Field of the Invention
The invention generally relates to an apparatus and a method for inspecting substrate internal defects.
2. Description of Prior Art
Semiconductor manufacturing processes such as thin film deposition are used for fabricating electronic components on a substrate. Accordingly, the quantity of internal defects in the substrate such as inclusions, bubbles, cracks is a critical factor indicating the quality of electronic components. In addition, cracks crack are generated on substrates because substrates undergo processes such as high temperature heating process and etching and are transported frequently in manufacturing processes.
Thus, inspecting internal defects on a substrate is an indispensable non destructive inspection. At present, the most frequently used crack inspection method arranges illuminating light sources beneath the substrate to emit light beam towards the lower surface of the substrate and penetrate the substrate, and uses a camera to obtain an image of the upper surface of the substrate above the substrate. The penetration rate of the light beam is reduced as the emitted light beam is reflected, refracted and scattered by internal defects. The image brightness of locations having internal defects is significantly lowered than other areas so that the locations and sizes of the internal defects can be identified by image analysis of human or computing devices subsequently.
The image definition of internal defects images determines the effectiveness of the inspection and efficiency of image analysis. Therefore, acquiring precise and clear images of internal defects has been an eager need to resolve in the inspection processes. Nonetheless, the above internal defects inspection has the following disadvantages. Firstly, as shown in the schematic diagram illustrating the above method for inspecting internal defects in FIG. 1, not only surface pollutants 11 adhered on two sides of a substrate 10 or the texture of the substrate 10 but also internal defects 12 such as inclusions or cracks would influence penetration rate of light beam during the manufacturing process. It is not effective to differentiate between internal defects 12 and surface pollutants 11 according to dark spots when interpreting images retrieved by a camera 30. Frequently, surface pollutants 11 are misinterpreted as internal defects 12.
As shown in FIG. 2, light beam diffracts as the light beam is interfered such that micro internal defects 12 in an image may be faded when emitting brightness of light beam become stronger. In other words, the image width of internal defects 12 is in inverse proportion to the light intensity. There are circumstances emitting light intensity is increased on a thicker substrate 10 in order to increase image brightness. Yet, when light intensity is higher than a certain level, light intensity of diffraction generated then becomes too strong which lowers the image definition of internal defects 12. Thus, it is required to spend higher cost on a camera with higher definition to retrieve clear image. In addition, under the circumstance when the tolerance of a substrate 10 is large, an optimal light intensity for retrieving the best image becomes a difficult decision. Further, as shown in FIG. 3, when crack width of micro defects 12 under non parallel light becomes smaller, it is difficult to enhance image definition of micro crack by projecting light from different directions. Photo of the attachment 1 is a photo of crack image taken by prior art method for inspecting defects.